From Contractional theory to modern geology

Modern Plate Tectonics is the Grand Unified Theory of modern geology, however like many other theories it developed slowly, and in it actual form is only 50 years old.Plate tectonics is essential to understand the shape and distribution of continents, the genesis of mountains and sedimentary basins, the structure of mountains, why earthquakes and volcanoes occur and how dangerous they can become.

Already after the first maps of the American continent were published (1507 and after) and become public, the similarity between the coast of Africa and America intrigued geographers and naturalists, and this fascination continued in the following centuries.In 1620 the English philosopher Francis Bacon noted the jigsaw form in his "Novum Organum" and claimed that "it's more then a curiosity", and 38 years later the munch Francois Placet published a small booklet entitled "The break up of large and small world's, as being demonstrated that America was connected before the flood with the other parts of the world." He argued that the two continents were once connected by the lost continent of "Atlantis", and the sin flood beaked them apart.The idea of the biblical flood explaining the shape of earth remained popular for the next 250 years.

Fig.1. Illustration from Thomas Burnet´s book "The Sacred Theory of the Earth", published in 1684, where he tries to explain the fitting shapes of the continents by the biblical flood. Parts of the crust of earth broke up (first drawing), releasing water from the underground. This water covers the entire planet (second drawing), and finally flowing back in the fissures leaves back a shattered crust that now forms islands and continents (last drawing).

The great French palaeontologist Buffon in his "Les Epoques de la Nature" (1717) not only addresses the age of earth, but also speculates about a former land bridge connecting Irland and America to explain the distribution of fossil shells found on both landmasses.The American president and naturalist Benjamin Franklin by trying to explain fossils found on the summits of mountains propose in a letter to French geologist Abbd J. L. Giraud-Soulavie in 1782:

“Such changes in the superficial parts of the globe seemed to me unlikely to happen if the earth were solid to the center. I therefore imagined that the internal parts might be a fluid more dense, and of greater specific gravity than any of the solids we are acquainted with, which therefore might swim in or upon that fluid. Thus the surface of the earth would be a shell, capable of being broken and disordered by the violent movements of the fluid on which it rested.”

The great German naturalist and geographer Alexander von Humboldt explored South America from 1799 until 1804, and observed that the similarities between the two coastlines were not only restricted to a morphological pattern, but also to the geological features: mountain chains that seemed to end on one continent continued on the other, the Brazilian highland remembers the landscape of Congo, the Amazonian basin has it's counterpart in the lowlands of Guinea, the mountain ranges of North America are - geologically - very similar to the old European mountains and rocks in Mexico resemble those found in Ireland.

Fig.2. Columnar Jointing in the basalts of Regla, Mexico, as depicted in Alexander von Humboldts (1810) „Pittoreske Ansichten der Cordilleren und Monumente amerikanischer Völker.“, the accompanying text explains:“The basalts of Regla, which are presented on this copper plate, are an incontrovertible proof of this identity of forms, which is noted on the rocks of different climates. Travelled mineralogist need only to look at this drawing to recognize the basalt forms in Vivarais, in the Euganean Mountains or in the foothills of Antrim, in Ireland. The smallest coincidences observed in the European rock-pillars are also found in this group of Mexican basalts. Such a great analogy let us assume a similar principle of formation acting under all climates in various temporal epochs, the basalts covered by compact limestone and clay-slate must be of different age than those who are resting on layers of coal and boulders."

But still the flood argument was a strong one, and so Humboldt argued that the Ocean represents a large, ancient river bed, flooded subsequently by the biblical catastrophe and forming the Atlantic Ocean.

The French zoologist Jean-Baptiste Lamarck (1744-1829) developed a surprisingly new hypothesis. To explain the discovery of fossil marine animals on the dry land he proposed that the continents "move" slowly, but irresistible, around the globe. The east coastlines of the single continents were eroded by the sea, but in the same rate new sediments were deposited on the west coast, so doing, the dry land in the past was a marine ground many times.Unfortunately, also for the lack of evidence for his theory, Lamarck was not able to find a publisher for his "Hydrogéologie", and printed in 1802 on his own behalf 1.025 copies, but only a small number of books could be sold.

The new century saw the birth a new hypothesis to explain the shape of Earth, the Contractional theory, formulated by the American geologist James Dwigth Dana (1813-1895), explained mountains and continents as products of a cooling and subsequently shrinking earth.After the theory of Dana the modern continents represent remnants of the former earth crust or at least the first parts of earth that solidified after the formation of the planet.The Austrian Geologist Eduard Suess published in his multi-volume work "Das Antlitz der Erde” (1883-1909) this hand coloured map, showing the primordial continent - "cores" today separated by younger during the contraction of Earth formed and today water filled basins. He also suggested that the deep-sea trenches along the border of the Pacific are zones where the ocean floor plunges beneath the continents.

Fig.3. Hand coloured map showing the primordial continent -"cores" according to the Austrian geologist Eduard Suess "Das Antlitz der Erde" (The Face of the Earth) published in various volumes in the years 1883 to 1909.

But the theory of Dana and other “earth contraction” supporters couldn’t explain the irregular distribution of mountain ranges on earth and why areas with strong tectonic movements and earthquakes alternate with "quiet" areas, according to this idea, such features had to be distributed randomly on the surface of a cooling and shrinking body.

George Darwin, the son of Charles R. Darwin, explained the formations of the continents as result of the detachment of the moon from earth 57 million years ago by centrifugal forces.The American geologist Frank Taylor in contrary tried to prove that the moon was captured by earth some 100 million years ago, and the resulting tide waves rip apart the single continent on the surface of the planet.

Antonio Snider-Pellegrini, an American scientist living in Paris, was the first in 1858 to publish a reconstruction of America and Africa forming a single continent. But in absence of a mechanism to explain such movements, he relayed again on the great flood, an obsolete idea even for those times.

Fig.4. This 1858 reconstruction by Antonio Snider-Pellegrini represents one of the first maps of a former supercontinent. In contrary to other naturalist of the time, Snider-Pellegrini assumed still a sudden and very fast movement, imputable to the biblical flood.

5 comments:

In the 1830s-1840s, Charles Darwin's subsidence theory of atoll formation was part of his larger thinking about ocean floor subsidence being complementary to uplift of mountains and continents - which we now know to be explainable in terms of plate tectonics. He and Charles Lyell developed and exchanged ideas about the mobility of the earth's crust, clearly envisaging the earth as a dynamic system. This led them also to speculate on mobility of the inner layers of the earth too. (Ref: this is discussed by Alistair Sponsel in his recent PhD dissertation at the University of Princeton (2009)).

Thanks for email. Yes this is the ref. I think it's a great bit of work, maybe even brilliant (but I'm a geologist/biologist not a historian). The full ref is:

Alistair William Sponsel, 2009. Coral reef formation and the sciences of earth, life and sea, c. 1770-1952. A dissertation presentedto the faculty pf Princeton University in candidacy of Doctor of Philosophy.

I have a pdf copy from the author, but as it's unpublished, I don't feel I could to pass it on to a third party without his prior permission, especially as he has been writing it up as book. Not sure how far he's got with that, though. Best if you wrote to him direct, at Harvard. You can find him on their website.

(FYI my own special interests are living and fossil corals and reefs, general and regional geology, biogeography, ecology and history of these subjects. http://bit.ly/ibtF62)

Thanks - yes I remember seeing your item on the Dolomites. I did write a comment but wasn't registered to comment at the time, so it got lost. I mentioned the Dolomites in my 1982 article on Darwin and coral reefs. You can find this on Darwin Online http://bit.ly/fAEtFA. For more on the photo in my article go to: http://www.flickr.com/photos/brize/3695916058/ & also http://www.flickr.com/photos/brize/3706858774/in/photostream/